1. Field of the Disclosure
Embodiments of the present invention are directed to noise-reduction measures for appliances and, more particularly, to an integrally-formed acoustic base tray for a dishwashing appliance and an associated method.
2. Description of Related Art
A dishwasher typically includes a wash tub for containing the dishware to be washed. However, the tub must also include surrounding structure and components to form the overall dishwasher assembly. The components, such as the various controls, valves, pumps, and the like are mounted outside the tub, but are included within the overall structure of the dishwasher assembly. Accordingly, the tub may be supported by an integrally-molded base, wherein the base is fastened to the tub in order to support the dishwasher assembly. Many of the various components are mounted to the base and under the tub. The base may be molded, for example, from a talc-filled polypropylene, and may include molded recesses and mounting surfaces for particular components such as the control board, valves, pumps, and the like. The base may also be molded to receive a cover member (i.e., a bottom cover or “base tray”) over the lower opening that, in instances of the dishwasher requiring service, may be removed from the bottom of the dishwasher to allow access to the various components received by the base.
The “enclosure” aspect afforded by the base tray with respect to the molded base may also contain noise generated by the various operational components of the dishwasher. In doing so, a foam rubber or other insulation layer may be applied externally to the base tray to facilitate the sound absorption/containment within the base. However, the foam rubber layer undesirably adds another component and associated expense to the manufacturing process. In addition, the foam rubber layer may not necessarily be effective in attenuating the frequencies of noise produced by the various components of the dishwasher. Still further, the foam rubber layer may be prone to detachment or damage, thereby reducing the noise reduction capabilities. In still other instances, the base tray/foam rubber layer may undesirably form a “reverberation chamber”with the base and thus may, in some cases, amplify the noise generated by dishwasher components.
In one instance, the dishwasher base tray may be configured as a flat plate, possibly molded of a polymeric material, and have structural ribs for stiffening the structure of the base tray. It was found, however, that such a structure tended to vibrate and resonate during operation of the dishwasher, thereby increasing the overall noise emanating from the unit. Multiple changes in design, material and material densities were performed to stiffen and/or reduce the noise level associated with the base tray. In this regard, one measure involved adding two dampening panels to reduce structure-borne (vibration) sound. Special mounting grommets were introduced to reduce structure-borne sound generated by the motor and transmitted/amplified by the motor bracket and the stiff base tray. However, the effects of these measures were found to be limited to absorbing/reducing sound waves directed toward the base in the range of between about 80 Hz and about 200 Hz. Sound waves reflected, refracted, emitted, and/or transmitted at higher frequencies by other operational components within the dishwasher did not appear to be attenuated. Thus, it was found that the base tray configured in this manner, including structural ribs, actually enhanced the sound/noise created, emitted, and transmitted by this component during operation of the dishwasher unit. Additional undesirable acoustic effects were found to be related to temperature and the stress associated therewith: a cold base tray tended to generate low tone (frequency) resonances, and a hot or heated base tray tended to generate mid tone (frequency) resonances.
Thus, there exists a need for a base tray for enclosing the base of an appliance, such as a dishwasher, wherein the base tray is capable of attenuating, dissipating, or otherwise reducing the sound/noise generated by the base tray itself or other components of the appliance during operation of the appliance, due to vibrations or other wave energy (e.g., heat) imparted thereto by operational components of the appliance. Such a solution should be relatively simple and cheap to implement, be robust and durable, and be readily reconfigurable in the event of changes in appliance components or operational conditions associated therewith.